The invention relates to a method of manufacturing an article of a synthetic resin which on at least a part of its surface has a metal layer provided by electroless deposition.
According to a conventional electroless metallization process, the surface of the article to be metallized is treated with an aqueous ammoniacal silver salt solution, and is then, or simultaneously, treated with a reduction agent for the metal salt used, as a result metal atoms depositing on the surface of the article to be covered.
An interesting method of electroless metallization is the so-called aerosol metallization in which the metal salt solution and the reduction agent are atomized simultaneously on the surface of the article to be metallized. For further details of this method reference may be made to "The Technology of Aerosol Plating" by Donald J. Levy in Technical Proceedings 51st Annual Convention American Electroplaters' Society, 14-18 June, St. Louis, 1964, pp. 139-149.
It is stated on page 141, left column of this literature reference that upon metallizing synthetic resins, the non-polar weakly-polar surface of the resin must first be treated chemically or electrically and then be sensitized with a reduction agent, such as SnCl.sub.2. The reduction agent initiates and accelerates the deposition of metal atoms, a first monolayer of deposited metal being formed. Various chemical treating agents are recorded in Table II on page 140 of the above-mentioned literature reference.
The chemical pretreatment of products of synthetic resin so as to make them better suitable for providing a metal mirror has been given much attention in literature.
Published Netherlands patent application No. 74.10.125, for example, states that polyamide resins are pretreated with a swelling agent which is also a reduction agent.
According to French Patent Specification No. 1.328.032 the surface of, for example, a polystyrene synthetic resin is treated with a sulphonating or hydroxylating agent or with polyphenols or aminophenols.
German Offenlegungsschrift No. 2,755,374 states that the surface of the synthetic resin is provided with a special adhering or top layer which comprises a hydrophilic synthetic resin mixture.
According to published Netherlands patent application No. 68.16.061 the synthetic resin to be metallized, such as an ABS (Acrylonitrile-Butadiene--Styrene) synthetic resin must comprise a basic nitrogen-containing polymer, in particular polyvinylpyridine. Finally, reference is made to U.S. Pat. No. 3,094,430 in which it is stated that upon silverplating acrylic synthetic resins the surface is pretreated with tannine acid. A sensitisation treatment with SnCl.sub.2 is not used in this method.
However, the adhesion of an electroless plated metal layer on non-polar or weakly polar synthetic resins remains troublesome. In the first-mentioned literature reference "The technology of aerosol plating" it is stated in this respect on page 141 left column, that the chemical forces between metal layer and synthetic resin surface are usually very weak and that a considerable improvement of the adhesion occurs when the synthetic resin surface is roughened.
It is the object of the invention to manufacture an article of synthetic resin having an electroless plated metal layer in which the metal layer adheres excellently to the surface of the article and in which the said surface is not etched and in particular is not roughened.